U.S. patent application number 15/768970 was filed with the patent office on 2018-10-11 for method for polishing wafer and polishing apparatus.
This patent application is currently assigned to SHIN-ETSU HANDOTAI CO., LTD.. The applicant listed for this patent is SHIN-ETSU HANDOTAI CO., LTD.. Invention is credited to Hiromasa HASHIMOTO, Naoki KAMIHAMA, Kazuya SATO.
Application Number | 20180290261 15/768970 |
Document ID | / |
Family ID | 58662499 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180290261 |
Kind Code |
A1 |
SATO; Kazuya ; et
al. |
October 11, 2018 |
METHOD FOR POLISHING WAFER AND POLISHING APPARATUS
Abstract
The present invention provides a method for polishing a wafer
including, after unloading and before loading to hold, a next wafer
to be polished: measurement to measure a depth PD.sub.t of a
concave portion of a template after taking out a polished wafer;
calculation to calculate a difference .DELTA.PD between the
measured depth PD.sub.t of the concave portion and a depth PD.sub.0
of the concave portion of the template before being used for
polishing; and adjustment to adjust polishing conditions for a next
wafer to be polished in accordance with the calculated difference
.DELTA.PD. Consequently, there are provided the method for
polishing a wafer and a polishing apparatus which enable adjusting
a fluctuation in flatness of each wafer caused due to a fluctuation
in numerical value of a pocket depth of a template.
Inventors: |
SATO; Kazuya;
(Nasushiobara-shi, JP) ; HASHIMOTO; Hiromasa;
(Nishigo-mura, JP) ; KAMIHAMA; Naoki;
(Nishigo-mura, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIN-ETSU HANDOTAI CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
SHIN-ETSU HANDOTAI CO.,
LTD.
Tokyo
JP
|
Family ID: |
58662499 |
Appl. No.: |
15/768970 |
Filed: |
October 17, 2016 |
PCT Filed: |
October 17, 2016 |
PCT NO: |
PCT/JP2016/004596 |
371 Date: |
April 17, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 49/12 20130101;
B24B 37/20 20130101; H01L 22/26 20130101; H01L 21/304 20130101;
B24B 37/013 20130101; B24B 37/34 20130101; H01L 21/30625 20130101;
B24B 37/042 20130101 |
International
Class: |
B24B 37/013 20060101
B24B037/013; B24B 37/04 20060101 B24B037/04; B24B 37/20 20060101
B24B037/20; B24B 49/12 20060101 B24B049/12; H01L 21/66 20060101
H01L021/66; H01L 21/306 20060101 H01L021/306 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2015 |
JP |
2015-218440 |
Claims
1-8. (canceled)
9. A method for polishing a wafer by which a plurality of wafers
are polished, with the use of a rotatable polishing head having a
template which has an annular member and a backing pad attached to
each other and has a concave portion to house and hold a wafer
formed therein by using an inner peripheral surface of the annular
member and a surface of the backing pad attached to the annular
member, by repeating loading to house and hold the wafer in the
concave portion, polishing to press the wafer held by the polishing
head against a polishing pad attached to an upper side of a
rotatable turntable for polishing while rotating the turntable and
the polishing head, and unloading to take out the polished wafer
from the concave portion of the template, wherein the method
comprises, after the unloading and before the loading to hold a
next wafer to be polished: measurement to measure a depth PD.sub.t
of the concave portion after taking out the polished wafer;
calculation to calculate a difference .DELTA.PD between the
measured depth PD.sub.t of the concave portion and a depth PD.sub.0
of the concave portion of the template before being used for
polishing; and adjustment to adjust polishing conditions for a next
wafer to be polished in accordance with the calculated difference
.DELTA.PD.
10. The method for polishing a wafer according to claim 9, wherein,
in the adjustment, an abrasion loss of the annular member during
polishing is adjusted in such a manner that the difference
.DELTA.PD decreases by adjusting one or both of a relative speed of
the number of revolutions of the turntable and the number of
revolutions of the polishing head and a polishing pressure.
11. The method for polishing a wafer according to claim 9, wherein,
in the adjustment, a plastic deformation amount of the backing pad
is adjusted in such a manner that .DELTA.PD decreases by changing
the backing pad to another backing pad having a different amount of
plastic deformation caused by the polishing pressure.
12. The method for polishing a wafer according to claim 10,
wherein, in the adjustment, a plastic deformation amount of the
backing pad is adjusted in such a manner that .DELTA.PD decreases
by changing the backing pad to another backing pad having a
different amount of plastic deformation caused by the polishing
pressure.
13. The method for polishing a wafer according to claim 9, wherein
the adjustment is performed when the difference .DELTA.PD between
the depth PD.sub.t and the depth PD.sub.0 has exceeded a
predetermined value.
14. The method for polishing a wafer according to claim 10, wherein
the adjustment is performed when the difference .DELTA.PD between
the depth PD.sub.t and the depth PD.sub.0 has exceeded a
predetermined value.
15. The method for polishing a wafer according to claim 11, wherein
the adjustment is performed when the difference .DELTA.PD between
the depth PD.sub.t and the depth PD.sub.0 has exceeded a
predetermined value.
16. The method for polishing a wafer according to claim 12, wherein
the adjustment is performed when the difference .DELTA.PD between
the depth PD.sub.t and the depth PD.sub.0 has exceeded a
predetermined value.
17. A polishing apparatus comprising: a rotatable polishing head
having a template which has an annular member and a backing pad
attached to each other and has a concave portion to house and hold
a wafer formed therein by using an inner peripheral surface of the
annular member and a surface of the backing pad attached to the
annular member; and a polishing pad attached to an upper side of a
rotatable turntable, the apparatus pressing the wafer held by the
polishing head against the polishing pad for polishing while
rotating the turntable and the polishing head, wherein the
polishing apparatus comprises: measuring means configured to
measure a depth PD.sub.t of the concave portion of the template
after taking out the polished wafer; calculating means for
calculating a difference .DELTA.PD between the measured depth
PD.sub.t of the concave portion and a depth PD.sub.0 of the concave
portion of the template before being used for polishing; and
adjusting means for adjusting polishing conditions for a next wafer
to be polished in accordance with the calculated difference
.DELTA.PD.
18. The polishing apparatus according to claim 17, wherein the
adjusting means adjusts an abrasion loss of the annular member
during polishing in such a manner that the difference APD decreases
by adjusting one or both of a relative speed of the number of
revolutions of the turntable and the number of revolutions of the
polishing head and a polishing pressure.
19. The polishing apparatus according to claim 17, wherein the
adjusting means adjusts the polishing conditions when the
difference .DELTA.PD between the depth PD.sub.t and the depth
PD.sub.0 has exceeded a predetermined value.
20. The polishing apparatus according to claim 18, wherein the
adjusting means adjusts the polishing conditions when the
difference .DELTA.PD between the depth PD.sub.t and the depth
PD.sub.0 has exceeded a predetermined value.
21. The polishing apparatus according to claim 17, wherein the
measuring means comprises: a sensor unit which measures the depth
PD.sub.t of the concave portion of the template from which the
polished wafer has been removed; and a movement unit which moves
the sensor unit to be placed below the template at the time of
measuring the depth PD.sub.t of the concave portion.
22. The polishing apparatus according to claim 18, wherein the
measuring means comprises: a sensor unit which measures the depth
PD.sub.t of the concave portion of the template from which the
polished wafer has been removed; and a movement unit which moves
the sensor unit to be placed below the template at the time of
measuring the depth PDt of the concave portion
23. The polishing apparatus according to claim 19, wherein the
measuring means comprises: a sensor unit which measures the depth
PD.sub.t of the concave portion of the template from which the
polished wafer has been removed; and a movement unit which moves
the sensor unit to be placed below the template at the time of
measuring the depth PD.sub.t of the concave portion.
24. The polishing apparatus according to claim 20, wherein the
measuring means comprises: a sensor unit which measures the depth
PD.sub.t of the concave portion of the template from which the
polished wafer has been removed; and a movement unit which moves
the sensor unit to be placed below the template at the time of
measuring the depth PD.sub.t of the concave portion.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for polishing a
wafer and a polishing apparatus.
BACKGROUND ART
[0002] Polishing of wafers is often performed by a waxless mount
polishing apparatus which contains a wafer in an annular member
made of, e.g., glass epoxy and holds a back side of the wafer by a
backing pad placed between the wafer and a polishing head. Usually,
to perform this polishing, a template having the annular member
bonded to the backing pad is used. The template is usually attached
to an annular base ring made of PVC (polyvinyl chloride), titanium,
or the like in the polishing head, and used in this state.
CITATION LIST
Patent Literatures
[0003] Patent Literature 1: Japanese Unexamined Patent Application
Publication No. 2004-23038
[0004] Patent Literature 2: Japanese Patent No. 4013187
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0005] In such waxless .mount type polishing as described above,
there is a phenomenon that a shape of a polished wafer changes in
correspondence with a use time of the template, and this is a
problem in stabilization, of flatness of the wafer.
[0006] In conventional examples, flatness of a polished wafer is
measured with respect such a change in shape of the wafer andf when
the measured flatness is below standards this problem is
sequentially tackled by e.g., replacing the template with a new one
or with a used template adopted in another apparatus so that the
flatness of the polished wafer can fail within the standards.
However, in case of dealing with a result of the measurement of the
flatness of the wafer; a time lag occurs in adjustment of the
flatness due to the replacement of the template, thus leading to
the wafer whose flatness is below standards. Further, if the
flatness fails within standards, any adjustment is not performed in
particular, and hence a variation in flatness of the wafer from an
initial stage to a terminal stage of a life of the template becomes
large.
[0007] As a result of studies, the present inventors have found out
that an aging variation of a pocket depth (which will be also
referred to as PD hereinafter which is a depth of a concave portion
in which a wafer is housed and held by an inner peripheral surface
of an annular member and a surface of backing pad which is attached
to the annular member concerns a flatness fluctuation corresponding
to a use trine of the template. Furthermore, they have acknowledged
that a main cause of the aging variation of the PD is abrasion of
the annular member and deformation of the backing pad. However, in
a conventional technology, the aging variation of the PD is not
taken into consideration, and the PD is measured before and after
attachment of the polishing head alone.
[0008] For example, Patent Literature 1 discloses that a protrusion
is provided on a surface of a retainer ring (an annular member) of
a template and a polishing pad is in-situ-dressed during polishing,
and flatness of a wafer is thereby stabilized. However, in this
patent literature, the flatness fluctuation due to abrasion of the
annular member and deformation of the backing pad is not taken into
consideration. Further, it has a description that ceramics having
abrasion resistance can be used as a material of the annular
member, but there arises a problem, e.g., occurrence of an
obstruction such that cracks are produced in a work edge portion at
an inner peripheral end when this material is used.
[0009] Further, Patent Literature 2 discloses that adjustment is
performed by inserting or removing a spacer having a thickness of
approximately 10 .mu.m between a main body of a polishing head and
a template in correspondence with a target wafer thickness.
However, it has no description on whether fine adjustment which
enables flatness control can be performed. Further, even if such
adjustment can be performed, an operation is troublesome, there is
no description about means for confirming a level difference, after
inserting/removing the spacer, and a flatness fluctuation due to
aging variation of PD is not taken into consideration.
[0010] In view of such a problem as described above, it is an
object of the present invention to provide a method for polishing a
wafer and a polishing apparatus which enable adjusting a
fluctuation in flatness of a wafer due to a fluctuation in
numerical value of a pocket depth of a template.
Means for Solving Problem
[0011] To achieve the object, the present invention provides a
method for polishing a wafer by which a plurality of wafers are
polished, with the use of a rotatable polishing head having a
template which has an annular member and a backing pad attached to
each other and has a concave portion to house and hold a wafer
formed therein by using an inner peripheral surface of the annular
member and a surface of the backing pad attached to the annular
member, by repeating loading to house and hold the wafer in the
concave portion, polishing to press the wafer held by the polishing
head against a polishing pad attached to an upper side of a
rotatable turntable for polishing while rotating the turntable and
the polishing head, and unloading to take out the polished wafer
from the concave portion of the template, the method being
characterized by including, after the unloading and before the
loading to hold a next wafer to be polished: measurement to measure
a depth PD.sub.t of the concave portion after taking out the
polished wafer; calculation to calculate a difference .DELTA.PD
between the measured depth PD.sub.t of the concave portion and a
depth PD.sub.0 of the concave portion of the template before being
used for polishing; and adjustment to adjust polishing conditions
for a next wafer to be polished in accordance with the calculated
difference .DELTA.PD.
[0012] With this arrangement, it is possible to appropriately
adjust the polishing conditions under which a fluctuation in
numerical value of the pocket depth of the template is measured and
a fluctuation in flatness of the wafer is adjusted (suppressed in
particular) in correspondence with this numerical value.
Consequently, a variation in flatness of the wafer corresponding to
a use time of the template can be reduced.
[0013] At this time, in the adjustment, an abrasion loss of the
annular member during polishing can be adjusted in such a manner
that the difference .DELTA.PD decreases by adjusting one or both of
a relative speed of the number of revolutions of the turntable and
the number of revolutions of the polishing head and a polishing
pressure.
[0014] In this mariner, when the polishing conditions are adjusted
in such a manner that the difference .DELTA.PD between PD.sub.t and
PD.sub.0 becomes small, i.e., that the depth of the concave portion
of the template does not fluctuation from an initial stage, a
variation in flatness of the wafer corresponding to a use time of
the template can be reduced.
[0015] Further, at this time, in the adjustment, a plastic
deformation, amount of the backing pad can be adjusted in such a
manner that .DELTA.PD decreases by changing the backing; pad to
another backing pad having a different amount of plastic
deformation caused by the polishing pressure.
[0016] In this manner, when the polishing conditions are adjusted
in such a manner that, the depth of the concave portion of the
template does not fluctuate from the initial stage, a variation in
flatness of the wafer corresponding to a use time of the template
cam be reduced.
[0017] Furthermore, the adjustment can be performed when the
difference .DELTA.PD between the depth PD.sub.t and the depth
PD.sub.0 has exceeded a predetermined value.
[0018] When it has been determined that the difference .DELTA.PD in
depth is larger than the predetermined value and flatness of a next
wafer to be polished can become larger than a preset threshold
value, performing the adjustment enables adjusting the polishing
conditions while suppressing a reduction in productivity and
enables reducing a variation in flatness.
[0019] Moreover, to achieve the object, the present invention
provides a polishing apparatus including: a rotatable polishing
head having a template which has an annular member and a backing
pad attached to each other and has a concave portion to house and
hold a wafer formed therein by using an inner peripheral surface of
the annular member and a surface of the backing pad attached to the
annular member; and a polishing pad attached to an upper side of a
rotatable turntable, the apparatus pressing the wafer held by the
polishing head against the polishing pad for polishing while
rotating the turntable and the polishing head, the polishing
apparatus being characterized by including: measuring means
configured to measure a depth PD.sub.t of the concave portion of
the template after taking out the polished wafer; calculating means
for calculating a difference .DELTA.PD between the measured depth
PD.sub.t of the concave portion and a depth PD.sub.0 of the concave
portion of the template before being used for polishing; and
adjusting means for adjusting polishing conditions for a next wafer
to be polished in accordance with the calculated difference
.DELTA.PD.
[0020] According to such a polishing apparatus, it is possible to
appropriately adjust the polishing conditions to polishing
conditions under which a fluctuation in numerical value of the
pocket depth of the template is measured and a fluctuation in
flatness of the wafer can be especially suppressed in
correspondence with the numerical value. Consequently, there is
provided the polishing apparatus which can reduce a. variation in
flatness of the wafer in correspondence with a use time of the
template.
[0021] At this time, it is preferable for the adjusting means to
adjust an abrasion loss of the annular member during polishing in
such a manner that the difference .DELTA.PD decreases by adjusting
one or both of a relative speed of the number of revolutions of the
turntable and the number of revolutions of the polishing head ana a
polishing pressure.
[0022] According to such a polishing apparatus, it is possible to
reduce a variation in flatness of the wafer corresponding to a use
time of the template by adjusting the polishing conditions in such
a manner that the depth of the concave portion of the template does
not fluctuate from the initial stage.
[0023] Additionally, at this time, it is preferable for the
adjusting means to adjust the polishing conditions when the
difference .DELTA.PD between the depth PD.sub.t and the depth
PD.sub.0 has exceeded a predetermined value.
[0024] When it has been determined that the difference .DELTA.PD in
depth is larger than the predetermined value and flatness of a next
wafer to be polished can become larger than a preset, threshold
value, performing the adjustment enables adjusting the polishing
conditions while suppressing a reduction in productivity and
enables reducing a variation in flatness.
[0025] Further, it is preferable for the measuring means to
include: a sensor unit which measures the depth PD.sub.t of the
concave portion of the template from which the polished wafer has
been removed; and a movement unit which moves the sensor unit to be
placed below the template at the time of measuring the depth
PD.sub.t of the concave portion.
[0026] The polishing apparatus according to the present invention,
the depth PD.sub.t of the concave portion can be measured by such
measuring means.
EFFECT OF THE INVENTION
[0027] According to the method for polishing a wafer and the
polishing apparatus of the present invention, a fluctuation in
flatness of a wafer can be suppressed by monitoring a fluctuation
in numerical value of the depth of the concave portion of the
template and adjusting polishing conditions in correspondence with
this numerical value.
BRIEF DESCRIPTION OF DRAWINGS
[0028] FIG. 1 is a schematic view showing an example of a polishing
apparatus according to the present invention;
[0029] FIG. 2 is a schematic view snowing an example of a mode at
the time of measuring a depth PD.sub.t of a concave portion by
measuring means of the polishing apparatus according to the present
invention;
[0030] FIG. 3 is a view describing a change in depth of the concave
portion of the template associated with use for polishing;
[0031] FIG. 4 is a flowchart showing an example of a method for
polishing a wafer according to the present invention;
[0032] FIG. 5 is a view showing an example of an imaging result
provided by an in-line type laser displacement gauge;
[0033] FIG. 6 is a graph showing an example of a measurement result
provided by the in-line type laser displacement gauge;
[0034] FIG. 7 shows a measurement result of PD.sub.t in Example
1;
[0035] FIG. 8 is a graph showing changes in number of revolutions
of a polishing head in Example 1;
[0036] FIG. 9 shows a measurement result of ESFQDmax in Example
1;
[0037] FIG. 10 is a measurement result of PD.sub.t in Comparative
Example;
[0038] FIG. 11 is a measurement result of ESFQDmax in Comparative
Example;
[0039] FIG. 12 is a measurement result of PD.sub.t in Example
2;
[0040] FIG. 13 is a measurement result of ESFQDmax in Example
2;
[0041] FIG. 14 is a measurement result of PD.sub.t in Example 3;
and
[0042] FIG. 15 is a measurement result of ESFQDmax in Example
3.
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0043] An embodiment, of the present invention will now be
described hereinafter, but the present invention is not restricted
thereto.
[0044] As described above, there is a problem that flatness of a
wafer fluctuates in correspondence with a use time of a template,
and a variation in flatness of the wafer increases.
[0045] Thus, the present inventors have repeatedly conducted the
earnest, examination to solve such a problem. Consequently, they
have found out that the fluctuation in flatness is mainly caused
due to a fluctuation in depth (PD) of a concave portion of the
template. Further, they have conceived that the variation in
flatness can be adjusted and, for example, suppressed by adjusting
polishing conditions while monitoring a value of PD, thereby
bringing the present invention to completion.
[0046] A polishing apparatus according to the present invention
will be first described hereinafter in detail with reference to
FIGS. 1 to 3, but the present invention is not restricted thereto.
As shown in FIG. 1, the polishing apparatus 1 according to the
present invention includes a rotatable polishing head 2 configured
to hold a wafer W, a rotatable turntable 3, and a polishing pad 4
attached to an upper side of the turntable 3. Furthermore, it may
also include a polishing agent supply mechanism 5 which supplies a
polishing agent to the polishing pad 4 at the time of polishing the
wafer W.
[0047] The polishing head 2 has a template 8 formed by attaching an
annular member 6 to a backing pad 7. As shown in FIG. 1, in the
template 8, an inner peripheral surface of the annular member 6 and
a surface of the backing pad 7 attached to the annular member 6
form a concave portion 9 in which the wafer W is housed and
held.
[0048] In this polishing apparatus 1, a back surface of the wafer W
is held by the backing pad 1, an edge portion of the wafer W is
held by the annular member 6, the polishing agent is supplied onto
the polishing pad 4 from the polishing agent supply mechanism 5,
and the wafer W is pressed to the polishing pad 4 while rotating
the turntable 3 and the polishing head 2 respectively, thereby
polishing the wafer W while being rubbed against the polishing pad
4.
[0049] Furthermore, the polishing apparatus 1 according to the
present invention includes measuring means 10 which can measure a
depth PD.sub.t of the concave portion 9 of the template 8 after
taking out the polished wafer W. The measuring means 10 has, e.g.,
a sensor unit 11 and a movement unit 12 which moves the sensor unit
11 to be placed below the template 8 at the time of measuring the
concave portion depth PD.sub.t.
[0050] As shown in FIG, 2, the sensor unit 11 can measure the depth
PD.sub.t of the concave portion 9 of the template 8 from which the
polished wafer W has been taken out, and. the movement, unit 12 can
move the sensor unit 11 to be placed below the template 8 at the
time of measuring the concave portion depth PD.sub.t.
[0051] As the sensor unit 11, an in-line type laser displacement
gauge can be used. As such, a displacement gauge, for example,
LJ-V7020 (manufactured by KEYENCE Corporation) can be used. As to
the measurement of PD.sub.t based on this system, a level
difference of the annular member 6 and the backing pad 7 is
line-scanned, a level difference between a reflected optical, image
from a surface of the annular member 6 and a reflected optical
image from a surface of the backing pad 7 can be measured as
PD.sub.t. Additionally, a cover may be provided to the sensor unit
11 to prevent droplets of the polishing agent from striking on the
sensor unit 11.
[0052] Further, as the movement unit 12, an X axis direction slider
which enables movement in an X axis direction (a horizontal
direction) can be used. A standby position of the sensor unit 11
during polishing the wafer W is a position which does not obstruct
the polishing, and the sensor unit 11 is moved to be placed below
the template 8 at the time of measuring the concave portion depth
PD.sub.t after unloading the wafer W. The position below the
template 8 is, e.g., a position, at which the level difference of
the annular member 6 and the backing pad 7 is included in a
measurement range of the sensor unit 11.
[0053] For example, the measuring means 10 may have a laser
displacement gauge disposed at a tip of the X axis direction
slider, and may be set so that the laser displacement gauge can
advance to a position below the template 8 and the laser
displacement gauge can retreat from the position below the template
8.
[0054] Furthermore, the polishing apparatus 1 includes calculating
means 13 which calculates .DELTA.PD which is a difference between
the depth PD.sub.t of the concave portion 9 measured by the
measuring means 10 and a depth PD.sub.0 of the concave portion 9 of
the template 8 before being used for polishing. As the calculating
means 13, a personal computer (PC) or the like can be used.
Moreover, it also includes adjusting means 14 which adjusts
polishing conditions for the next wafer W to be polished in
accordance with the difference .DELTA.PD calculated by the
calculating means 13.
[0055] According to such a polishing apparatus 1 of the present
invention, the depth PD.sub.t of the concave portion 9 of the
template 8 is measured, and the polishing conditions can be
appropriately adjusted to polishing conditions which enable
particularly suppressing a fluctuation in flatness of the wafer W
in correspondence with the difference .DELTA.PD between PD.sub.t
and PD.sub.0. Additionally, since the adjustment can be performed
based on a value of PD.sub.t before obtaining a flatness
measurement result after the polishing, a course of changes in
flatness can be corrected with a smaller time lag, and hence a
variation in flatness of the wafer from an initial stage to a
terminal stage of a life of the template can be suppressed.
[0056] Further, to reduce a variation in flatness of the wafer W,
more specifically, it is preferable for the adjusting means 14 to
adjust an abrasion loss of the annular member 6 at the time of the
polishing so that the difference .DELTA.PD can decrease by
adjusting one or both of a relative speed of the number of
revolutions of the turntable 3 and the number of revolutions of the
polishing head 2 and a polishing pressure. When an amount of change
of the depth PD.sub.t of the concave portion 9 from the concave
portion depth PD.sub.0 on the initial stage is reduced, a variation
in flatness of the wafer W can be decreased. The reason will be
described hereinafter.
[0057] As shown in FIG. 3, before the template 8 is used for
polishing, i.e., when a use time t of the template 8 for polishing
is 0, the depth PD.sub.0 of the concave portion 9 is equal to a
thickness of the annular member 6 on the initial stage. However, as
shown in FIG. 3, two elements, i.e., an abrasion loss A of the
annular member 6 and a plastic deformation amount P of the backing
pad 7 are added to the depth PD.sub.t of the concave portion 9
v/hen t>0. That is, the depth PD.sub.t of the concave portion 9
when t>0 is expressed as PD.sub.t=PD.sub.0--A+P.
[0058] According to this expression, it can be understood that
PD.sub.t is shallower than PD.sub.0 when A>P, PD.sub.t is deeper
than PDo when A<P, and PD.sub.t is equal to PD.sub.0 when A=P.
Thus, the expression means that sag of the wafer advances when
A>P, rise of the same advances when A<P, and a fluctuation in
flatness of the wafer corresponding to the use time of the template
8 hardly occurs when A-P, respectively.
[0059] As described above, the expression means that, when
-A+P.fwdarw.0, PD.sub.t.fwdarw.PD.sub.0 is achieved, and PD.sub.t
can be maintained at a value closer to PD.sub.0 even after the life
of the template 8 has proceeded. That is, when a magnitude relation
between A and P is controlled and the difference .DELTA.PD between
PD.sub.t and PD.sub.0 is reduced, a variation in flatness of the
wafer can be decreased.
[0060] Here, since A is an abrasion loss (or an abrasion rate) of
the annular member 6, it can be adjusted by using a relative speed
of the numbers of revolutions of the polishing head 2 and the
turntable 3 or a polishing pressure. On the other hand, since P is
a plastic deformation amount of the backing pad 7, it. can be
adjusted by using the polishing pressure, a compression ratio of
the backing pad 7, or the like. With such adjustments, when
-A+P.fwdarw.0 can be achieved, namely, when PD.sub.t can be
controlled to a value which is close to PD.sub.0 as much as
possible, a fluctuation in flatness of the wafer based on the use
time t of the template can be reduced. Furthermore, since the
rotational speeds of the turntable 3 and the polishing head 2 or
the polishing pressure can be changed by varying a polishing
recipe, the rotational speed or the polishing pressure can be
adjusted without replacing the template 8, and hence a .reduction
in productivity can be suppressed.
[0061] Moreover, in the polishing apparatus 1 according to the
present invention, when the difference .DELTA.PD between the depth
PD.sub.t and the depth PD.sub.0 exceeds a predetermined value, the
adjusting means 14 can adjust the polishing conditions. With such
arrangement, a fluctuation in flatness of the wafer can be reduced
while avoiding a reduction in productivity.
[0062] The method for polishing a wafer according to the present
invention will now be described with reference to an example using
the polishing apparatus 1 of the present invention.
[0063] FIG. 4 shows a flowchart of an example of the method for
polishing a wafer according to the present invention. First,
disposing the template 8 to the polishing head 2 is performed.
Then, measurement of the depth PD.sub.0 of the concave portion 9 of
the template 8 before being used for polishing is carried out.
Subsequently, loading to house and hold the wafer W in the concave
portion 9, polishing to press the wafer W held by the polishing
head 2 against the polishing pad 4 attached to the upper side of
the rotatable turntable 3 and to polish the wafer W while rotating
the turntable 3 and the polishing head. 2, and unloading to take
out the polished wafer W from the concave portion 9 of the template
are performed.
[0064] Then, the measuring means 10 is used to perform measurement
to measure the depth PD.sub.t of the concave portion 9. At this
time, it is preferable to perform the measurement, at the timing
when the polishing head 2 is placed at an elevated position after
the polishing is finished and the wafer W is unloaded from the
polishing head 2. Further, an in-line type laser displacement gauge
can be used for the measurement to measure the depth PD.sub.t of
the concave portion 9, FIG. 5 shows an example of an imaging result
of one line. In this manner, the depth PDt of the concave portion 9
can be measured from a level difference between reflected optical
images from surfaces of the annular member 6 and the backing pad
7.
[0065] Furthermore, after the sensor unit 11 is advanced to a
position where PD.sub.t can be measured, the sensor can be linked
with rotation of the polishing head to acquire a line profile in
accordance with each angle by using a servo motor which drives the
polishing head 2 to rotate and an external synchronization signal,
and a distribution of PD.sub.t in a radial direction of a lower
surface of the template can be digitized. Measurement data is
output to, e.g., a monitor of the PC. Here, FIG. 6 shows an example
of the measurement data. "Displacement from reference surface" on
an axis of ordinate in a graph of FIG. 6 represents a displacements
(mm) of each, measurement point from a specific reference surface,
and "angle" represents an angle (.degree.) of each of the annular
member and the backing pad from each reference position in a
circumferential direction. An average value of PD.sub.t in the
radial direction in the concave portion may be calculated from the
thus digitized distribution of PD.sub.t.
[0066] Subsequently, the calculating means 13 performs calculation
to calculate the difference .DELTA.PD between the measured depth
PD.sub.t of the concave portion 9 and the depth PDo of the concave
portion 9 of the template 8 before being used for polishing. The
measurement value of PD.sub.t is compared with PD.sub.0 every time
the measurement is performed in this manner.
[0067] Then, the adjusting means 14 or the like is used to perform
the adjustment to adjust the polishing conditions for the next
wafer to be polished in accordance with the calculated difference
.DELTA.PD. In the method for polishing a wafer according to the
present invention, in the adjustment, when one or both of a
relative speed of the number of revolutions of the turntable 3 and
the number of revolutions of the polishing head 2 and a polishing
pressure are adjusted, an abrasion loss of the annular member 6
during the polishing can be adjusted in such a manner that the
difference .DELTA.PD decreases. Further, in the adjustment, when
the backing pad 7 is changed to another backing pad whose plastic
deformation amount differs depending on the polishing pressure, the
plastic deformation amount of the backing pad can be adjusted in
such a manner that the difference APD decreases,
[0068] Furthermore, in the present invention, the adjustment can be
carried out when the difference .DELTA.PD between the depth
PD.sub.t and the depth PD.sub.0 has increased to be larger than a
predetermined value. More specifically, for example, as an index of
a change in magnitude of the difference .DELTA.PD, a provision can
be set to a rate of change of the depth PD.sub.t from PD.sub.0 to
determine whether the adjustment is to be performed. It is to be
noted that the rate of change can be defined as, e.g., (rate of
change)-[(PD.sub.t-PD.sub.0)/PD.sub.0].times.100. Moreover, upper
and lower-limit values of the rate of change can be set down in
correspondence with a flatness standard. That is, the upper and
lower limit values of the rate of change can be set so that
flatness in a desired range can be provided.
[0069] Here, for example, a description will be given as to a case
where .+-.3% is determined as each of the upper and lower limit
values and the relative speed or the polishing pressure is adjusted
as the polishing conditions. In this case, when (rate of change)
>+3% is achieved, it can be determined that an outer peripheral
portion of a wafer further rises, and also estimated that the
flatness of the wafer becomes below the standard. Thus, the
polishing conditions for the next wafer are adjusted so that the
relative speed of the polishing head and the turntable is raised or
the polishing pressure is raised to increase the abrasion loss A of
the annular ring. To raise the relative speed, for example, the
number of revolutions of the polishing head is increased or the
number of revolutions of the turntable is decreased when the number
of revolutions of the turntable is smaller than the number of
revolutions of the polishing head.
[0070] On the other hand, when (rate of change)<-3% is achieved,
it can be determined that the outer peripheral portion of the wafer
further sags, and also estimated that the flatness of the wafer
becomes below the standard. Thus, the polishing conditions for the
next wafer are adjusted so that the relative speed of the polishing
head and the turntable is decreased or the polishing pressure is
decreased to reduce the abrasion loss A of the annular ring. To
decrease the relative speed, for example, the number of revolutions
of the polishing head is decreased or the number of revolutions of
the. turntable is increased when the number of revolutions of the
turntable is smaller than the number of revolutions of the
polishing head. When the rate of change falls within the range of
the upper and lower limit values, the operation can be continued
under the same polishing conditions. After the polishing conditions
are adjusted in this manner, the next wafer is loaded and
polished.
[0071] Additionally, the measurement and the calculation may be
performed each time after the unloading or they may be performed
in, e.g., each fixed cycle while repeating the loading to the
unloading more than once. A frequency of the measurement and the
calculation can be appropriately determined while considering an
accuracy of required flatness, productivity, and the like.
[0072] As described above, according to the method for polishing a
wafer of the present invention, a fluctuation in flatness of each
wafer can be adjusted, or especially suppressed by appropriately
adjusting the polishing conditions in correspondence with the
difference .DELTA.PD between the depths PDt.sub.t and PD.sub.0.
EXAMPLES
[0073] The present invention will now be more specifically
described hereinafter with reference to examples and a comparative
example of the present invention, but the present invention is not
restricted thereto.
Example 1
[0074] A template with PD.sub.0.apprxeq.700 .mu.m was disposed to
such a polishing head of a polishing apparatus according to the
present invention as shown in FIG. 1, and silicon wafers were
continuously polished in accordance with the flow shown in FIG.
4.
[0075] Further, a life of the template was determined as 450 hours,
and flatness of each wafer and PD.sub.t were measured every 50
hours. PD.sub.t was measured by LJ-V7020(manufactured by KEYENCE
Corporation). Furthermore, in Example 1, .+-.3% of a rate of change
of PD.sub.t from. PD.sub.0 was determined as each of upper and
lower limit values, and polishing conditions were adjusted when the
rate of change had become out of this range.
[0076] Specifically, when the rate of change had become out of this
range, in Example 1, a relative speed of a turntable and the
polishing head was adjusted by increasing or decreasing the number
of revolutions of the head, thereby controlling an abrasion loss A
of an annular member. The number of revolutions of the polishing
head in the initial stage was set to 20 rpm. The number of
revolutions of the turntable was fixed at a value smaller than the
number of revolutions of the polishing head.
[0077] As shown in FIG. 7, PD.sub.t was monotonously increased
until a use time of the template reached 200 hours. Furthermore,
when the use time of the template had reached 200 hours, the rate
of change exceeded +3% as the upper limit value. Thus, as shown in
FIG. 8, the number of revolutions of the polishing head was changed
from. 20 rpm to 40 rpm. to increase the abrasion loss A of the
annular member. Consequently, as shown in FIG. 7, after 200 hours,
PD.sub.t changed to decrease, and the difference .DELTA.PD became
small.
[0078] The flatness of each polished wafer was measured by
Wafersight manufactured by KLA-Tencor Corporation, it was confirmed
by using a maximum value ESFQDmax of ESFQD (Edge Site Front least
sQuares <site> Deviation). It is to be noted that ESFQDmax is
an index which represents a rise shape of an outer periphery when
it is a positive value or a sag shape of the same when it is a
negative value.
[0079] FIG. 9 shows a result of measuring ESFQDmax of each wafer
every 50 hours. ESFQDmax was monotonously increased until the use
time of the template reached 200 hours like PDt, but the polishing
conditions were adjusted in accordance with the difference PD, and
then this value was thus reduced.
Comparative Example
[0080] Basically, polishing was performed in the same manner as
Example 1, but a depth of a concave portion was measured before
disposing a template to a polishing head and after removing the
template in Comparative Example. That is, like conventional
examples, polishing conditions were not adjusted in accordance with
am aging variation of the depth of the concave portion, and the
number of revolutions of the polishing head was set to 2 0 rpm from
beginning to end. The number of revolutions of a turntable was
fixed like Example.
[0081] Consequently, as shown in FIG. 10, the depth PD.sub.t of the
concave portion after end of polishing (after 450 hours) rose to
740 .mu.m. Furthermore, as shown in FIG. 11, ESFQDmax kept
monotonously increasing, and a rise shape greatly advanced as
compared with Example 1.
Example 2
[0082] After end of Example 1, polishing conditions were adjusted
in adjustment based on data of .DELTA.PD obtained in Example 1 in
such a manner that .DELTA.PD can further decrease by continuously
polishing of subsequent silicon wafers and flatness of polished
silicon wafers can be further improved. Specifically, wafers were
polished under the same conditions as those of Example 1 except
that a template was replaced with a template having a smaller
plastic deformation amount of a backing pad and the number of
revolutions of a polishing head was set to 20 rpm. The plastic
deformation amount of the backing pad was adjusted by changing a
material of the backing pad to reduce a compression ratio by 50%,
Moreover, in Example 2, .+-.1% of a rate of change of PD.sub.t from
PD.sub.0 was set as each of upper and lower limit values.
[0083] Consequently, as shown in FIG. 12, the rate of change of
PD.sub.t was .+-.1% or less from beginning to end, and a
fluctuation in PD.sub.t was a half or less of that in Comparative
Example. Additionally, as shown in FIG. 13, an increased amount of
ESFQDmax was also a half or less of that in Comparative Example.
Further, averages of fluctuations in PD.sub.t and .DELTA.PD were
reduced as compared with Example 1, and an average of ESFQDmax was
also reduced. Consequently, it was confirmed that a variation in
flatness can be further suppressed by repeatedly performing the
polishing and adjusting the plastic deformation amount of the
backing pad in correspondence with data of .DELTA.PD by the
polishing method according to the present invention.
Example 3
[0084] After end of Example 2, based on the data of .DELTA.PD
obtained in Examples 1 and 2, polishing conditions were again
adjusted in the adjustment in such a manner that .DELTA.PD could be
further decreased and flatness could be improved by continuously
polishing subsequent silicon wafers. Specifically, the same backing
pad as that in Example 2 was used, the number of revolutions of a
polishing head was optimized, and the initial number of revolutions
of the polishing head was adjusted to 25 rpm. As for the rest, the
wafers were polished under the same, conditions as those in Example
2.
[0085] Consequently, as show in. FIG. 14, a rate of change of
PD.sub.t was .+-.1% or less from beginning to end, and a.
difference from PD.sub.0 was hardly produced. Furthermore, as shown
in FIG. 15, an amount of change in ESFQDmax was the smallest among
Examples, Consequently, it was confirmed that the polishing method
according to the present invention enables further suppressing a
variation in flatness by repeatedly performing polishing and
adjusting both a relative speed of the numbers of revolutions of a
turntable and the polishing pad and a plastic deformation amount of
the backing pad in correspondence with, the data of .DELTA.PD.
[0086] Table 1 shows conditions and implementation results in
Examples 1 to 3 and Comparative Example as a whole. It is to be
noted that average values and standard deviations of PD.sub.t and
ESFQDmax are average values and standard deviations of aggregate
data from an initial stage to a terminal, stage of a life of a
template.
TABLE-US-00001 TABLE 1 Number of revolutions PD.sub.t ESFQDmax of
Backing pad PD.sub.0 [.mu.m] [.mu.m] polishing compression A P
[.mu.m] Standard Standard head [rpm] ratio [ratio] [.mu.m] [.mu.m]
Average Average deviation Average deviation Comparative 20 1 17 50
699 719.5 28.99138 0.01335 0.006429 Example Example 1 20-40 1 45 48
701 711.2 7.315129 0.0062 0.005453 Example 2 20 0.5 17 25 701 704.3
1.418136 0.0044 0.002914 Example 3 25 0.5 26 25 700 699.9 1.100505
0.0024 0.002366
[0087] As can be understood from Table 1, in each of Examples 1 to
3, a difference between A and P was reduced., and the difference
.DELTA.PD of PD.sub.t from PDo was controlled to be small f and
hence the average and the standard, deviation of ESFQDmax were also
suppressed to small values as compared, with Comparative Example.
That isf a fluctuation in flatness of each wafer was able to be
suppressed by adjusting the polishing conditions in accordance with
APD in each of Examples 1 to 3.
[0088] It is to be rioted that the present invention is not.
restricted to the embodiment. The embodiment is an illustrative
example, and any example which has substantially the same structure
and exerts the same functions and effects as the technical scope
described in claims of the present invention is included in the
technical scope of the present invention.
* * * * *